A deficit of normal tissue in a subject may result from, for example, burns, tumor resection surgery (e.g. mastectomy), or congenital deformities. Often, the tissue in deficit is skin and/or underlying connective tissue. The tissue in deficit can also be an intrabody duct (e.g. urethras or GI tract).
One method of correcting skin deficit is to stimulate creation of new skin. Implantation of a device that expands and stretches the existing skin causes a growth response in which new skin is created. While the exact physiologic mechanism of this response is not fully understood, clinical success has been reported for many years.
The formal concept of surgical tissue expansion was first reported by Neumann in 1957, in which a rubber balloon, attached to a percutaneous tube, was implanted to enable intermittent expansion for the purpose of reconstructing a partially amputated ear. The concept of tissue expansion was further refined and popularized for breast reconstruction by Radovan and Argenta in the 1980's. Despite many advantages of the technique, most notably minimal additional surgical dissection and patient downtime, the out-patient process remains lengthy and onerous, often involving months of weekly office visits and discomfort resulting from the relatively high pressures associated with periodic expansion by filling with saline. Most commercially available tissue expanders function as an implantable balloon with a separate or imbedded valve that allows periodic filling. Typically, a physician performs the filling procedure. The filling events are relatively infrequent (e.g., weekly), and therefore a significant expansion pressure is typically applied at each doctor's visit to achieve a maximum effect from each visit. As a result of this expansion pressure during a clinic visit, a relatively sudden tissue stretch occurs. This may cause subjects to suffer discomfort and/or tissue ischemia. The relatively large expansion pressure can also adversely affect underlying structures, such as causing concavities in underlying bone. In addition, high pressure may create restrictive capsules around the implant and/or cause tissue failure. Some previously available alternatives used a percutaneous needle for inflation or filling or inflation, creating a potential source of infection.
Gradual, continuous expansion was introduced and thought to overcome many of the drawbacks associated with periodic saline injections. For example, osmotic expanders have been reported by Austad in 1979, Berge in 1999, and Olbrisch in 2003 (see U.S. Pat. Nos. 5,005,591 and 5,496,368). A commercial version is available from Osmed Corp. in a limited range of sizes. These devices use a polymeric osmotic driver to expand a silicone implant by absorbing interstitial fluid (“ISF”). A potential problem of such devices is the lack of control or adjustability after implantation with respect to expansion variables such as pressure, volume, onset of expansion, and end of expansion once they have been deployed. U.S. Pat. No. 6,668,836 to Greenberg et al. describes a method for pulsatile expansion of tissue using an external hydraulic pump. The external hydraulic pump is bulky and inconvenient for patients. The percutaneous attachment reduces patient mobility and may be a source of contamination. U.S. Pat. No. 4,955,905 to Reed teaches an external monitor for pressure of an implanted fluid filled tissue expansion device. U.S. Pat. Nos. 5,092,348 and 5,525,275 to Dubrul and Iverson, respectively, teach implantable devices with textured surfaces. Some other devices use mechanical or electromechanical forces to avoid having to use fluids for tissue expansion.
Widgerow tested a continuous expansion device using an external pump connected through tubing to the implanted expander that allowed complete patient control. This provided rapid time courses and patient satisfaction. However, the connector tubing imparts both a cumbersome setup for the patient as well as the fear that prolonged connection between the external environment and the implanted device may lead to contamination. As the expanded space ultimately receives a permanent implant, any level of contamination is considered unacceptable.
Despite the advent and acceptance of breast conservation treatment modalities for breast cancer, mastectomy remains the treatment of choice for breast cancer in several clinical settings. These include situations in which there is an inability to achieve clean margins without unacceptable deformation of the remaining breast tissue, multiple primary tumors, previous chest wall irradiation, pregnancy, or severe collagen vascular diseases (e.g., lupus). Mastectomy is also indicated for women at high risk due to the presence of BRCA1 or BRCA2 or contralateral disease. Many such women are candidates for breast reconstruction and opt for reconstructive surgery at the time of mastectomy or in a delayed fashion after healing. According to the American Society of Plastic Surgery statistics, 57,102 U.S. patients underwent breast reconstruction in 2007.
Prosthetic reconstruction of the breast, as a staged procedure with tissue expanders followed by implants, is a reliable method for breast reconstruction that offers favorable aesthetic and psychological results while adding only minimal additional surgical intervention. Today, the process usually involves the placement of a tissue expander device under the pectoralis major muscle and remaining skin of the absent breast. The device is then gradually inflated over several weeks or months by periodic injections of saline, causing the stretching and expansion of the overlying skin and muscle coverage. When adequate coverage is achieved, the expansion device is typically removed, and a permanent breast implant is placed into the expanded space.
A significant clinical advantage would be realized if tissue expanders, such as breast tissue expanders, could provide any or all of the following: the elimination of technical problems associated with earlier devices while allowing greater patient comfort, control, speed, overall user friendliness, continuous or near continuous expansion, complete surgeon-patient control, and the eradication of percutaneous communication with the external environment which can lead to infection.